Fix #521: provide longitude before latitude when calling query.lonlat_box

[grisaitis]

See signature of siphon.DataQuery.lonlat_box: https://github.com/Unidata/siphon/blob/a6529fbaf3165f93cdffa87080295431a647df2c/siphon/http_util.py#L174

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The following items must be addressed before the code can be merged. Please don't hesitate to ask for help if you're unsure of how to accomplish any of the items below:

• Closes issue ForecastModel.set_query_latlon provides arguments in the wrong order to query.lonlat_box. Longitude should precede latitude.  #521
• I am familiar with the contributing guidelines.
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• Code quality and style is sufficient. Passes git diff upstream/master -u -- "*.py" | flake8 --diff
• New code is fully documented. Includes sphinx/numpydoc compliant docstrings and comments in the code where necessary.
• Pull request is nearly complete and ready for detailed review.

[wholmgren]

@grisaitis do you want to add your name or username to the contributors list at the bottom of the whatsnew file?